SINKING OF THE PANTHEON.
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building the Pantheon at Paris. * In this edifice, a vastand lofty dome was to be supported by four groups ofelegant columns. In order to give the columns the ap-pearance of consisting only of a single stone, the drums,or truncated conical pieces of which the shafts were form-ed, were hollowed out towards the centre, so that theedges of every two pieces might unite closely all round,and not leave the least visible separation. The aspect ofthese columns, when first erected, was beautiful; theyappeared a chef-d'oeuvre of art : but when the immenseweight of the arch was laid on them, the edges of thedrums, which alone were in contact, not having sufficientsurface to support the pressure, split and crumbled away,and the whole dome settled down till all the surfaces ofeach joining came into contact. The architect found itnecessary to erect some large massy pillars in the centreof each group of columns which supported the dome,and the beauty of the structure disappeared. It wouldhave been preserved, had the joinings of the drums beensurfaces applied to each other in every point. Geometry supplies us with the means of doing this, in the mostsimple as well as in the most complicated cases.
Let us draw very correctly the curvilinear edges AB, BC, CD ,DA, ab, be, cd, da, fig. 3, pi. 10, of an arch stone. We can determinefor each face of the joint a developable surface, which passes throughboth AB and ab, one for BC and be, one for CD and cd, and one forDA and da. By doing the same for the adjacent stones, we may besure that the faces in contact will apply to each other in everypoint. When we know the position and figure of AB and ab, of BCand be, it will be very easy to employ the method already given, fig.2, to determine each developable surface.
When a large superficies is to be covered with theleaves of any very thin and flexible substance, these
* Formerly the Church of St. Genevieve. “ The dome of thePantheon, ” say Mr. Scott ," towers above all in light graceful pride;it arrests the eye of the spectator by the boldness of its elevation,and detains it by the gracefulness of its construction .”—(Visit to